Dehydrogenation of hydrocarbons in the presence of oxygen, chlorine and a group vi-b catalyst



United States Patent '6) 3,306,950 DEHY'DROGENATHON F HYDRGCARBONS INTHE PRESENCE OF OXYGEN, CHLGRHQE AND A GROUP VI-B CATALYST LajrnonisBajars, Princeton, Nl, assignor to Petro-Tex Chemical Corporation,Houston, Tex a corporation of Delaware No Drawing. Filed June 11, 1965,Ser. No. 463,363 16 Claims. (Cl. 260-680) This application is acontinuation-in-part of my earlier filed copending application SerialNumber 244,276, filed December 13, 1962, entitled DehydrogenationProcess now US. Patent No. 3,207,811, which in turn was acontinuation-in-part of my earlier filed application Serial Number36,718, filed June 17, 1960, entitled Dehydrogenation Process, nowabandoned. This application also contains subject matter of my earlierfiled applications Serial Number 145,992 and Serial Number 145,993, bothfiled October 18, 1961, and now abandoned.

This invention relates to a process for dehydrogenating organiccompounds.

The invention is suitably carried out by passing a mixture in criticalproportions, of the compound to be dehydrogenated, chlorine or achlorine-liberating compound, and oxygen, at a temperature of at least450 C., and at an organic compound partial pressure equivalent to lessthan about one-fifth atmosphere at a total pressure of one atmosphere inthe presence of hereinafter defined catalysts of the Periodic TableGroup VI-B to obtain the corresponding unsaturated organic compoundderivative of the same number of carbon atoms.

Suitable hydrocarbons to be dehydrogenated according to the process ofthis invention are aliphatic hydrocarbons of 4 to 6 carbon atoms andpreferably are selected from the group consisting of mono-olefins ordiolefins of 4 to 6 carbon atoms, saturated aliphatic hydrocarbons of 4to 6 carbon atoms and mixtures thereof. Examples of feed materials arebutene-l, cis-butene-Z, trans-butBne-Z, 2- methyl butene-3, Z-methylbutene-l, Z-methyl butene-2, n-butane, isobutane, butadiene-1,3, methylbutane, 2- methyl pentene-l, Z-methyl pentene-Z and mixtures thereof.For example, n-butane may be coverted to a mixture of butene-l andbutene-Z or may be converted to a mixture of butene-l, butene2 and/orbutadiene-1,3. A mixture of n-butane and butene-Z may be converted tobutadiene-1,3 or a mixture of butadiene-1,3 together with some butene-Zand butene-l. n-Butane, butene-l, butene-Z or butadiene-1,3 or mixturesthereof may be converted to vinyl acetylene. The reaction temperaturefor the production of vinyl acetylene is normally within the range ofabout 600 C. to 1000 C., such as between 650 C. and 850 C. Isobutane maybe converted to isobutylene. The Z-methyl butenes such as Z-methylbutene-l may be converted to isoprene. Excellent starting materials arethe four carbon hydrocarbons such as butene-l, cis or trans butene-Z,n-butane, and butadiene-l,3 and mixtures thereof. Useful feeds asstarting materials may be mixed hydrocarbon streams such a refinerystreams. For example, the feed material may be the olefin-containinghydrocarbon mixture obtained as the product from the dehydrogenation ofhydrocarbons. Another source of feed for the present process is fromrefinery by-products. For example, in the production of gasoline fromhigher hydrocarbons by either thermal or catalytic cracking apredominantly hydrocarbon stream containing predominantly hydrocarbonsof four carbon atoms may be produced and may comprise a mixture ofbutenes together with butadiene, butane, isobutane, isobutylene andother ingredients in minor amounts. These and other refinery by-productswhich contain normal ethylenically unsaturated hydrocarbons are usefulas start- 33%{950 Patented Feb. 28, 1967 ing materials. Another sourceof feedstock is the product from the dehydrogenation of butane tobutenes employing the Houdry Process. Although various mixtures ofhydrocarbons are useful, the preferred hydrocarbon feed contains atleast 50 weight percent butene-l, butene- 2, n-butane and/orbutadiene-1,3 and mixtures thereof, and more preferably contains atleast percent n-butane, butene-l, butene-Z and/or butadiene-1,3 andmixtures thereof. Any remainder usually will be aliphatic hydrocarbons.Cyclic hydro-carbons of 6 to 9 carbon atoms are also suitable but lesspreferred, such as the dehydrogenation of cyclohexane to cyclohexeneand/of benzene and the dehydrogenation of ethyl benzene to styrene, andthe like. The process of this invention is particularly efiective indehydrogenating aliphatic hydrocarbons having a straight carbon chain ofat least 4 carbon atoms to provide a product wherein the majorunsaturated product has the same number of carbon atoms as the feedhydrocarbon.

The chlorine-liberating material may be such as chlorine itself,hydrogen chloride, alkyl chlorides of 1 to 4 carbon atoms such as methylchloride or ethylene dichloride, carbon tetrachloride, ammoniumchloride, volatile metalioid chlorides, aromatic chlorides such asphenyl chloride, heterocyclic chloride, such as cyclohexyl chloride, andthe like. Preferably the chlorine-containnig material will eithervolatilize or decompose at a temperature of no greater than C. toliberate the required amount of chlorine or hydrogen chloride. Theamount of chlorinc must be at least 0.001 or 0.005 mol, and usually anamount of at least 0.01 mol of chlorine per mol of organic compound tobe dehydrogenated will be used. It is one of the unexpected advantagesof this invention that only very small amounts of chlorine are required.Less than 0.5 mol of chlorine, as 0.2 mol, per mol of organic compoundto be dehydrogenated may be employed. Suitable ranges are such as fromabout .005 or 0.01 to 0.05, 0.1 or 0.25 mol of chlorine per mol of thecompound to be dehydrogenated. Excellent results are obtained when thechlorine is present in an amount of less than 0.3 mol of chlorine permol of the compound to be dehydrogenated. It is understood that when aquantity of chlorine is referred to herein, both in the specificationand the claims, that this refers to the calculated quantity of chlorinein all forms present in the vapor space under the conditions of reactionregardless of the initial source or the form in which the chlorine ispresent. For example, a reference to 0.05 mol of chlorine would refer tothe quantity of chlorine present whether the chlorine was fed as 0.05mol of C1 or 0.10 mol of HCl. Preferably, the chlorine will be presentin an amount no greater than 5 or 10 mol percent of the total feed tothe dehydrogenation zone, including any diluents.

The minimum amount of oxygen employed will generally be at least aboutone-four mol of oxygen per mol of organic compound to be dehydrogenated.Large amounts as about 3 mols of oxygen per mol of organic compound maybe used. Excellent yields of the desired unsaturated derivatives havebeen obtained with amounts of oxygen from about 0.4 to about 1.0 or 1.5mols of oxygen per mol of organic compound and suitably may be withinthe range of about 0.4 to 2 mols of oxygen per mol of organic compound.Preferably, the oxygen will be present in an amount of at least 0.6 molper mol of compound to be dehydrogenated. Oxygen may be supplied to thereaction system as oxygen diluted with inert gases 'such as helium,carbon dioxide, as air and the like. In relation to chlorine, the amountof oxygen employed should be greater than 1.50

' ratio of the mols of oxygen to the mols of chlorine will gram mols ofoxygen per gram atom be greater than 4 or 5 mols of oxygen per mol ofchlorine, such as between 6 or 8 and 500 or about and 300 mols of oxygenper mol of chlorine.

The total pressure on systems employing the process of this inventionnormally will be at or in excess of atmospheric pressure but vacuum maybe used. Higher pressures, such as about 100 or 200 p.s.i.g. may beused. The initial partial pressure of the organic compound to bedehydrogenated under reaction conditions is critical and is preferablyequivalent to below about one-fifth atmosphere (or about 6 inches ofmercury absolute) when the total pressure is atmospheric to realize theadvantages of this invention and more preferably equivalent to nogreater than 3 or 4 inches of mercury absolute. Also, because theinitial partial pressure of the hydrocarbon to be dehydrogenated isequivalent to less than about 6 inches of mercury at a total pressure ofone atmosphere, the combined partial pressure of the hydrocarbon to bedehydrogenated plus the dehydrogenated hydrocarbon will also beequivalent to less than about 6 inches of mercury. For example, ifbutene is being dehydrogenated to butadiene, at no time will thecombined partial pressure of the butene and butadiene be greater thanequivalent to about 6 iinches of mercury at a total pres sure of oneatmosphere. The desired pressure is obtained and maintained bytechniques including vacuum operations, or by using helium, organiccompounds, nitrogen, steam and the like, or by a combination of thesemethods. Steam is particularly advantageous and it is surprising thatthe desired reactions to produce high yields of product are effected inthe presence of large amounts of steam. When steam is employed, theratio of steam to hydrocarbon to be dehydrogenated is normally withinthe range of about 4 or 5 to or mols of steam per mol of hydrocarbon,and generally will be between 8 and 15 mols of steam per mol ofhydrocarbon. The degree of dilution of the reactants with steam,nitrogen and the like is related to keeping the partial pressure ofhydrocarbon to be dehydrogenated in the system equivalent to preferablybelow 6 inches of mercury at one atmosphere total pressure. For example,in a mixture of one mol of butene, three mols of steam and one mol ofoxygen under a total pressure of one atmosphere, the butene would havean absolute pressure of one-fifth of the total pressure, or roughly sixinches of mercury absolute pressure. Equivalent to this six inches ofmercury butene absolute pressure at atmospheric pressure would be butenemixed with oxygen and chlorine under a vacuum such that the partialpressure of the butene is six inches of mercury absolute. A combinationof a diluent such as steam together with a vacuum may be utilized toachieve the desired partial pressure of the hydrocarbon. For the purposeof this invention, also equivalent to the six inches of mercury buteneabsolute pressure at atmospheric pressure would be the same mixture ofone mol of butene, three mols of steam and one mol of oxygen under atotal pressure greater than atmospheric, for example, a total pressureof 15 or 20 inches mercury above atmospheric. Thus, when the totalpressure on the reaction zone is greater than one atmosphere, theabsolute values for the pressure of butene will be increased in directproportion to the increase in total pressure above one atmosphere.Another feature of this invention is that the combined partial pressureof the hydrocarbon to be dehydrogenated plus the chlorine-liberatingmaterial Will also be equivalent to less than 6 inches of mercury, andpreferably no greater than 3 or 4 inches of mercury, at a total pressureof one atmosphere. The lower limit of hydrocarbon part al pressure willbe dictated by commercial considerations and practically will be greaterthan about 0.1 inch mercury.

The temperature of reaction may be at least 450 C. and preferably willbe at least about 500 C. The temperature of the reaction is from about450 C. to temperatures as high as 850 C. or 1000 C. The optimumtemperature is normally determined as by thermocouple at the maximumtemperature of the reaction. Usually the temperature of reaction will befrom at least or greater than 450 C. to about 750 C. or 900 C. Excellentresults have been obtained in the range of about 550 C. to 750 C., or500 C. to 850 C. At the higher temperatures vinyl acetylene may beproduced from 4 carbon hydrocarbon feed such as butene or butadiene. Thetemperatures are measured at the maximum temperature in the reactor.

The flow rates of the gaseous reactants may be varied quite widely andorganic compound gaseous flow rates ranging from about 0.1 to about 5liquid volumes of organic compound per volume of reactor packing perhour have been used. Generally, the fiow rates will be within the rangeof about 0.10 to 25 or higher liquid volumes of the compound to bedehydrogenated, calculated at standard conditions of 0 C. and 760 mm. ofmercury per volume of reactor space containing catalyst per hour(referred to as either LHSV or liquid v./v./hr.). Usually the LHSV willbe between 0.15 and 15. The volume of reactor containing catalyst isthat volume of reactor space including the volume displaced by thecatalyst. For example, if a reactor has a particular volume of cubicfeet of void space, when that void space is filled with catalystparticles, the original void space is the volume of reactor containingcatalyst for the purpose of calculating the flow rates. The residence orcontact time of the reactants in the reaction zone under any given setof reaction conditions depends upon the factors involved in thereaction. Contact times ranging from about 0.001 or 0.01 to about onesecond or higher, such as 5 or 10 or 20 seconds, have been found to besatisfactory. A preferred range is from 0.001 to 5 seconds. Residencetime is the calculated dwell time of the reaction mixture in thereaction zone, assuming the mols of production mixture are equivalent tothe mols of feed mixture. For the purpose of calculation of residencetimes, the reaction zone is the portion of the reactor containingcatalyst.

The manner of mixing the chlorine or chlorine-liberating compound,organic compound to be dehydrogenated, oxygen containing gas, and steam,if employed, is subject to some choice. In normal operations, theorganic compound may be preheated and mixed with steam and preheatedoxygen or air, and chlorine or hydrogen chloride are mixed therewithprior to passing the stream in vapor phase over the catalyst bed.Hydrogen chloride or a source of chlorine may be dissolved in water andmay be mixed with steam or air prior to reaction. Any of the reactantsmay be split and added incrementally. For example, part of the chlorinematerial may be mixed with the hydrocarbon to be dehydrogenated and theoxygen The mixture may then be heated to efiect some dehydrogenation andthereafter the remainder of the chlorine material added to effectfurther dehydrogenation. The hydrocarbon product is then suitablypurified as by fractionation to obtain the desired high purityunsaturated product.

For conducting the reaction, a variety of reactor types may be employed.Fixed bed reactors may be used and fluid and moving bed systems areadvantageously applied to the process of this invention. In any of thereactors suitable means for heat removal may be provided. Tubularreactors of small diameter may be employed and large diameter reactorswhich are loaded or packed with packing materials are very satisfactory.

Excellent results have been obtained by packing the reactor with thedefined catalyst particles as the method of introducing the catalyticsurface. The size of the catalyst particles may vary widely butgenerally the maximum particle size will at least pass through a TylerStandard Screen which has an opening of 2 inches, and generally thelargest particles of catalyst will pass through a Tyler Screen with oneinch openings. Very small particle size carriers may be utilized withthe only practical objection being that extremely small particles causeexcessive pressure drops across the reactor. In order to avoid highpressure drops across the reactor, generally at least 50 percent byWeight of the catalyst will be retained by a mesh Tyler Standard Screenwhich has openings of inch. However, if a fiuid bed reactor is utilized,catalyst particles may be quite small, such as from about 10 to 300microns. Thus, the particle size when particles are used preferably willbe from about 10 microns to a particle size which will pass through aTyler Screen with openings of 2 inches. If a carrier is used, thecatalyst may be deposited on the carrier by methods known in the artsuch as by preparing an aqueous solution or dispersion of the describedcatalyst, mixing the carrier with the solution or dispersion until theactive ingredients are coated on the carrier. The coated particles maythen be dried, for example, in an oven at about 10 C. Various othermethods of catalyst preparation known to those skilled in the art may beused. When carriers are utilized, these will be approximately of thesame size as the final coated catalyst particle, that is, for fixed bedprocesses the carriers will generally be retained on 10 mesh TylerScreen and will pass through a Tyler Screen with openings of 2 inches.Very useful carriers are Alundum, silicon carbide, Carborundum, pumice,kieselguhr, asbestos, and the like. The Alundums or other aluminacarriers are particularly useful. When carriers are used, the amount ofcatalyst on the carrier will generally be in the range of about 5 to 75weight percent of the total weight of the active catalyt c material pluscarrier. The carriers may be of a variety of shapes, including irregularshapes, cylinders or spheres. Another method for introducing therequired surface is to utilize as a reactor a small diameter tubewherein the tube wall is catalytic or is coated with catalytic material.If the tube wall is the only source of catalyst generally the tube wallwill be of an internal diameter of no greater than one inch such as lessthan /4 inch in diameter or preferably will be no greater than about /2inch in diameter. Other methods may be utilized to introduce thecatalytic surface such as by the use of rods, wires, mesh or shreds andthe like of catalytic material. The technique of utilizing fluid bedslends itself well to the process of this invention.

In the descriptions below of catalyst compos tions, the compositiondescribed is that of the surface which is exposed in the dehydrogenationzone to the reactants. That is. if a catalyst carrier is used, thecomposition described as the ca alyst refers to the compo ition of thesurface and not to the total composition of the surface coating pluscarrier. The catalytic compositions are intimate combinations ormixtures of the ingredients. These ingredients may or may not bechcmcally combined or alloyed. inert catalyst binding agents or fillersmay be used. but these will not ordinarily exceed about percent orpercent by weight of the catalytic surface exposed to the reactiongases.

The amount of solid catalyst utilized may be varied depending upon suchvariables as the activity of the catalyst, the amount of chlorine andoxygen used, the flow rates of reactants and the temperature ofreaction. The amount of catalyst will be present in an amount of gr aterthan 25 square feet of catalyst surface per cubic foot of reaction zonecontaining catalyst. Generally the ratios will be at least 40 squarefeet of catalyst surface per cubic foot of reaction zone. The catalystis more effectively utilized when the catalyst is present in an amountof at least square feet of catalyst surface per cubic foot of reactionZone containinng catalyst, and preferably the ratio of catalyst sufaceto Volume will be at least 120 square feet of catalyst surface per cubicfoot of reaction zone containing catalyst. Of course, the amount ofcatalyst surface may be much greater when irregular surface catalystsare used. When the catalyst is in the form of particles, eithersupported or unsupported, the amount of catalyst surface may beexpressed in terms of the surface area per unit weight of any particularvolume of values for the surface to weight ratio are such as about- /2to 200 square meters per gram, although higher and lower values may beused.

The catalyst of this invention will be a metal or metal compound of thePeriodic Table Group VI-B, and mixtures thereof. The group is based onthe conventional long form of the Periodic Table as found on pages 400and 401 of the 39th edition (1957-58) of the Handbook of Chemistry andPhysics (Chemical Rubber Publishing Company). The metals of the GroupVI-B and compounds thereof such as the salts, oxides, or hydroxides areeffective catalysts. Particularly effective are inorganic compounds suchas the oxides, phosphates, and the halides, such as the iodides,bromides, chlorides and fiuorides. Useful catalysts are such aschromium, chromic chloride, chromic oxide, molybdenum trioxide,molybdenum phosphate, tungsten trioxide, tungstic acid, activatedalumina containing chromium' oxide coated thereon, chromium phosphate,and the like. Mixtures of the metal or metal compounds may be used. Alsomixtures of salts, such as halides, and oxides may be employed.Preferably the catalyst will be solid under the conditions of reaction.Excellent catalysts are those comprising atoms of chromium, molybdenum,and tungsten, such as the oxides, iodides, bromides, chlorides, orfluorides of these elements. Many of the salts, oxides and hydroxides ofthe metals may change during the preparation of the catalyst, duringheating in a reactor prior to use in the process of this invention, orare converted to another form under the described reaction conditions,but such materials still function as an effective compound in thedefined process. For example, many of the metal nitrates, nitrites,carbonates, hydroxides, acetates, and the like may be converted to thecorresponding oxide or chloride under the reaction conditions definedherein. Such salts as the phosphates, sulfates, halides, and the like,of the defined metal group, which may be stable or partially stable atthe defined reaction temperatures are likewise effective under theconditions of the described reaction, as Well as such compounds whichare converted to another form in the reactor. When reference is made inthe specification or claims to the catalyst being inorganic, this meansthat the catalyst is inorganic under the conditions of reaction and doesnot mean that organic precursors are excluded. Other suitable compoundsare such as the sulfites, silicates and sulfides. At any rate, thecatalysts are effective if the Group VI-B elements are present'in acatalytic amount in contact with the reaction gases. The metal oxidesrepresent the preferred class of materials. The oxides may be formed insitu from "arious salts and hydroxides. The catalysts of this inventionare solid at room temperature or are essentially solid under theconditions of reaction (although some volatilization may occur).

In the following examples will be found specific embodiments of theinvention and details employed in the practice of the invention. LHSV(or liquid v./v./hr.) means, with reference to the flow rate of oragniccornpound to be dehydrogenated, liquid volume of organic compound perhour per volume of packing or active surface material in the reactionZone. Percent conversion represents mols of organic compound consumedper mols of organic compound fed to a reactor and percent selectivityrepresents the mols of organic compound consumed. These examples areintended as illustrative only since numerous modifications andvariations in accordance with the disclosure herein will be apparent tothose skilled in the art. All quantities of chlorine expressed arecalculated as mols of C1 Example 1 A Vycor 2 reactor, which is filledwith inch Vycor Raschig rings having deposited thereon the hereinafterdesignated metal compounds, is heated by means of an external electricfurnace. The rings are coated with the metal oxides from water slurriesthereof and dried before use in a stream of air. At a 700 C. furnacetemperature, in a series of runs, butene-2 is used at a flow rate of oneliquid v./v./hr., mixed with oxygen and steam at mol ratios of butene tosteam to oxygen of l to 16 to 0.85. Hydrogen chloride is added as a 37percent aqueous solution at a rate which is equivalent to 0.115 mol ofchlorine (C1 per mol of butene-2. Butene and oxygen are added to the topof the reactor, hydrogen chloride is added to this stream thereafter asit enters the reactor, and steam is added separately opposite thisstream. When using a molybdenum oxide catalyst, a yield of 35 molpercent butadiene is produced.

Example 2 Example 1 is repeated using a 20 percent chromic oxide onalumina to give a yield of 39 percent per pass.

Example 3 Example 1 is repeated using a tungstic acid catalyst. Theconversion of butene is 73 percent.

Chlorine is suitably used to replace HCl in these examples. When theabove examples are repeated using the same reaction conditions andmolybdenum oxide on a support as Alundum as a reactor packing,isobutylene is obtained from isobutane and isoprene is obtained fromZ-methyl butene-2.

Example 4 The run is made in a Vycor reactor which is one inch internaldiameter; the overall length of the reactor is about 36 inches with themiddle 24 inches of the reactor being encompassed by a heating furnace;the bottom 6 inches of the reactor is empty, at the top of this 6 inchesis a retaining plate; and on top of this plate are placed 6 inches ofthe catalyst particles. The remainder of the reactor is filled with thecatalyst. The flow rates are calculated on the volume of the 6 inch longby 1 inch diameter portion of the reactor which is filled with catalystparticles. The Vycor reactor is packed with molybdenum sesquisulfide. Ata 700 C. maximum bed temperature, a 5050 mol percent mixture of n-butaneand butene-2 is dehydrogenated to n'butene and butadiene-1,3. The flowrate of hydrocarbon is maintained at /2 liquid volume of hydrocarbon(calculated at C. and 760 mm. mercury) per volume of reactor packed withcatalyst per hour (lv./v./hr.). Oxygen and steam are also fed to thereactor in the same stream at a mol ratio of oxygen to hydrocarbon of1.0, and a mol ratio of steam to hydrocarbon of 15. Hydrogen chloride isadded to the inlet to the reactor as an aqueous solution at a rate whichis equivalent to 0.08 mol of chlorine (calculated as C1 per mol ofhydrocarbon. The hydrocarbon and oxygen are added to the top of thereactor and the aqueous solution of hydrogen chloride is added to thisstream as it enters the reactor. The steam is added separately in a linewhich is opposite the hydrogen chloride inlet line.

Example Z-methyl butene-2 is dehydrogenated to isoprene employing atungsten oxide catalyst. The flow rate is 0.2 LHSV and steam, oxygen andHCl are fed in molar ratios of 15, 1.0 and .05 (calculated as C1respectively.

2 Vycor is the trade name of Corning Glass Works. Corning, i\'.Y., andis composed of approximately 96 percent silica with the remainder beingessentially B203.

8 Example 6 n-Butane is dehydrogenated in a series of runs utilizingvarious catalysts. The runs were made in a one-inch diameter Vycorreactor. The overall length of the reactor is approximately 14 inches,and 12 inches of the center portion of the reactor is surrounded by anelectrical heating furnace. At the bottom of the reactor are placed afew /4" x A" Vycor Raschig rings. On top of the Raschig rings, andWithin the portion of the reactor surrounded by the heating furnace, isplaced 50 cc. of the designated catalyst. The remainder of the reactoris filled with A" x /4 Vycor Raschig rings to form a preheat zone. Theflow of the gases through the reactor is from the top to the bottom. Thevarious catalysts are present in the reactor deposited on 3 diameteralumina spheres as supports (Norton Co. SA-52l8). The catalyst ischarged to the reactor as the oxide. The metal oxide is slurried indistilled water, and the alumina spheres to be used as the carrier areimmersed in the slurry in order to form the coating. The combination ofthe carrier and the slurry is heated in a rotating glass beaker which issurrounded by a heater. The particles are tumbled and heated until thecatalyst particles are dry enough to flow freely. The maximumtemperature of the catalyst particles in this heater is no greater thanapproximately C. Thereafter, the catalyst particles are transferred toan oven and heated at about C. to further dry the particles(approximately 4 hours).

The runs are made at an oxygen to butane ratio of 1.30 mols of oxygen(fed as air) per mol of butane and at a chlorine to butane ratio of 0.30mol C1 (fed as chlorine). Nitrogen is present in the feed in an amountof 15 mols per mol of butane. The flow rate of butane is .25 liquidhourly space velocity. The maximum temperature in the reactor is 550 C.Under these conditions and utilizing a chromium oxide catalyst, then-butane is dehydrogenated to a mixture of n-butene and butadiene- 1,3at a total selectivity of about 55 mol percent.

Example 7 Example 6 is repeated with the exception that molybdenum oxideis used as the catalyst. The total selectivity to butene and butadiene(plus a minor portion of heavier materials not separated) is 88.5 molpercent.

Example 8 Example 6 is repeated with the exception that W0 issubstituted as the catalyst. The total selectivity to butene andbutadiene is 86.5 mol percent, with the selectivity to heavier products(including any chlorinated hydrocarbons) being only 8.4 mol percent.

From the foregoing description of the invention, it will be seen that anovel and greatly improved process is provided for producing unsaturatedcompounds of lower molecular weight but of the same number of carbonatoms as the feed. Other examples could be devised for a process wherebythe catalyst contained the described elements, preferably with thedescribed elements constituting greater than or at least fifty atomicweight percent of any cations in the surfaces exposed to the reactiongases. Excellent catalysts are obtained when the defined catalyticmaterials are the main active constituent in the catalyst. Also, thecatalysts may consist essentially of the defined catalytic materials.Although representative embodiments of the invention have beenspecifically described, it is not intended or desired that the inventionbe limited solely thereto since it will be apparent to those skilled inthe art that modifications and variations may be made without departingfrom the spirit and scope of the invention. The products such asbutadiene-1,3 have many well known uses such as raw materials for theproduction of synthetic rubber.

I claim:

1. The method for dehydrogenating aliphatic hydrocarbons of 4 to 6carbon atoms which comprises heating in the vapor phase at a temperatureof from about 450 C. to 850 C. an aliphatic hydrocarbon of 4 to 6 carbonatoms with oxygen in a molar ratio of at least one-fourth mol of oxygenper mol of said hydrocarbon and chlorine in a molar ratio of from atleast 0.001 to less than 0.5 mol of chlorine per mol of saidhydrocarbon, the partial pressure of said hydrocarbon being equivalentto less than about one-fifth atmosphere at a total pressure of oneatmosphere, in the presence of a catalyst comprising a material selectedfrom the group consisting of chromium, molybdenum, tungsten and mixturesthereof in an amount greater than fifty atomic weight percent of anycations in the catalyst surface exposed to the reaction gases, the ratioof the gram mols of the said oxygen to the gram atoms of said chlorinebeing at least 1.50.

2. The method of claim 1 wherein the said hydrocarbon contains fourcarbon atoms.

3. The method of claim 1 wherein the catalyst comprises molybdenumoxide.

4. The method of claim 1 wherein the catalyst comprises chromium oxide.

5. The method of claim 1 wherein the catalyst comprises tungsten oxide.

6. The method of claim 1 wherein the said hydrocarbon is n-butene.

7. The method of claim 1 wherein the said hydrocarbon comprisesn-butane.

3. The method of claim 1 wherein the oxygen is present in an amount offrom about 0.4 to 2 mols of oxygen per mol of said hydrocarbon.

9. The method of claim 1 wherein the chlorine is present in an amount offrom at least 0.01 mol of chlorine to 0.2 mol of chlorine per mol ofsaid hydrocarbon.

10. The method of claim 1 wherein the vapor phase contains from about 4to 30 mols of steam per mol of said hydrocarbon.

11. The method of claim 1 wherein the catalyst is present as an oxide.

12. The method of claim 1 wherein the catalyst is present as a chloride.

13. The method of claim 1 wherein the catalyst is present as aninorganic salt.

14. The method for dehydrogenating aliphatic hydrocarbons of 4 to 6carbon atoms which comprises heating in the vapor phase at a temperatureof from about 450 C. to 850 C. the corresponding hydrocarbon of 4 to 6carbon atoms with oxygen in a molar ratio of from about 0.4 to 2 mols ofoxygen per mol of said hydrocarbon and chlorine in a molar ratio of fromat least 0.01 mol of chlorine to 0.2 mol of chlorine per mol of saidhydrocarbon, the partial pressure of said hydrocarbon being equivalentto less than about one-fifth atmosphere at a total pressure of oneatmosphere, in the presence of a catalyst comprising a member selectedfrom the group consisting of chromium, molybdenum, tungsten and mixturesthereof in an amount greater than fifty atomic weight percent of anycations in the catalyst surface exposed to the reaction gases, the ratioof the gram mols of said oxygen to the gram atoms of said chlorine beingat least 1.50.

'15. The method of claim 14 wherein the said catalyst comprises oxidesof the said member selected from the group consisting of chromium,molybdenum, tungsten and mixtures thereof.

16. The method of dehydrogenation of n-butene-Z which comprises heatingin the vapor phase at a temperature of about 550 C. to 750 C. butene-2with oxygen in an amount of about 0.85 mol of oxygen per mol of butene-2and about 0.115 mol of chlorine per mol of butene-2 and about 16 mols ofsteam per mol of butene-2 with a tungsten oxide catalyst.

References Cited by the Examiner UNITED STATES PATENTS 2,326,258 8/1943Schmidt et al. 260680 2,370,513 2/1945 Amos et al. 260680 2,945,9007/1960 Alexander et al. 260680 3,028,440 4/ 1962 Arganbright 260-6803,173,962 3/1965 Carroll et al 260-680 3,205,280 9/1965 Wattimena et al.260860 3,207,805 9/1965 Gay 260-680 3,207,811 9/1965 Bajars 260-6803,210,436 10/1965 Bajars et al. 260680 PAUL M. COUGHLAN, JR., PrimaryExaminer.

1. THE METHOD FOR DEHYDROGENATING ALIPHATIC HYDROCARBONS OF 4 TO 6CARBON ATOMS WHICH COMPRISES HEATING IN THE VAPOR PHASE AT A TEMPERATUREOF FROM ABOUT 450* C. TO 850*C. AN ALIPHATIC HYDROCARBON OF 4 TO 6CARBON ATOMS WITH OXYGEN IN A MOLAR RATIO OF AT LEAST ONE-FOURTH MOL OFOXYGEN PER MOL OF SAID HYDROCARBON AND CHLORINE IN MOLAR RATIO OF FROMAT LEAST 0.001 TO LESS THAN 0.5 MOL OF CHLORINE PER MOL OF SAIDHYDROCARBON, THE PARIAL PRESSURE OF SAID HYDROCARBON BEING EQUIVALENT TOLESS THAN ABOUT ONE-FIFTH ATMOSPHERE AT A TOTAL PRESSURE OF ONEATMOSPHERE, IN THE PRESENCE OF A CATALYST COMPRISING A MATERIAL SELECTEDFROM THE GROUP CONSISTING OF CHROMIUM, MOLYBDENUM, TUNGSTEN AND MISTURESTHEREOF IN AN AMOUNT GREATER THAN FIFTY AOMIC WEIGHT PERCENT OF ANYCATIONS IN THE CATALYST SURFACE EXPOSED TO THE REACTION GASES, THE RATIOOF THE GRAM MOLS OF THE SAID OXYGEN TO THE GRAM ATOMS OF SAID CHLORINEBEING AT LEAST 1.50.